A Magnetic Resonance Imaging (MRI) unit consists of a large cylindrical superconducting magnet for generating a strong magnetic field, devices for transmitting and receiving radio waves, and a complex computer system. When a patient lies inside the MRI unit, the strong magnetic field causes the hydrogen nuclei in the patient to line up. A low-frequency radio wave is pulsed through the magnet into the patient. The hydrogen atoms absorb the energy released by the radio waves. This disrupts the uniformity of the nuclei. When the radio-wave stimulation stops, the nuclei return to their original state and emit energy in the form of weak radio frequency (RF) signals. The strength and length of these RF signals—and therefore the kind of image produced—depend on the properties of the organ or tissue involved. A computer translates the RF signals into highly detailed cross-sectional images. The images are essentially maps of the locations of water or hydrogen in the body.
The magnetic field produced by the MRI unit constrains installation of associated MRI equipment. In particular, any ferromagnetic object near the MRI unit will be attracted by the magnetic field, either impairing operation of the equipment or becoming a safety hazard if forcibly projected toward the MRI unit. Also, the uniformity of the magnetic field of the MRI unit is altered by ferromagnetic material, even if the ferromagnetic material is secured to prevent safety hazards. Consequently, ferromagnetic material is generally kept away from the MRI unit.
The radio frequency transmissions emitted by the MRI unit toward the patient also poses electromagnetic interference/compatibility (EMIC) constraints on the installation of other equipment. General consumer and medical equipment such as personal computers and monitors are typically inadequately shielded to prevent impairment of function due to the strength of such RF emissions. Inversely, the MRI unit is susceptible to degraded performance if RF noise from other equipment distorts the received RF signal during imaging.
For these reasons, the core of the MRI unit, including the magnetic field producing and RF transmission and receiving portions, is placed within a magnet room that is shielded from the other rooms of the MRI suite and the rest of the facility. Often, nonferrous metal sheets or mesh encompass the entire magnet room to prevent magnetic energy and RF energy from entering or leaving the magnet room. Consequently, the MRI unit generally includes highly shielded electrical power, data and control cabling that are routed through filtered and grounded access points so that susceptible or interfering components of the MRI unit may be placed outside of the shielded room.
The same installation constraints affect installation of other equipment in the shielded magnet room. For example, utility electrical power, typically provided as AC outlets throughout the facility, are a transmission path for RF noise and are thus often not provided in the shielded magnet room. Similarly, sensors and controls for equipment used in the MRI suite often have to be placed in another room of the MRI suite, typically either an equipment room or control room. These controls are connected to the magnet room via a penetration panel that maintains the EMI shielding while allowing penetration by shielded and filtered electrical cables.
As MRI units became capable of increased computational speed, opportunities were presented for use of contrast media, injected into patients before or during an MRI scan, to enhance dynamic imaging studies. In addition, contrast media were developed that allowed MRI scanning of certain types of tissues that otherwise were insufficiently distinguishable from surrounding tissue for effective MRI diagnostic studies. Power injectors for contrast media are sometimes preferred due to repeatability of dosage volumes and injection rates and keeping personnel away from the MRI unit during a scan. However, adapting contrast media injectors from other radiological modalities (e.g., X-ray, Computer-aided Tomography (CT), etc.) was difficult due to MRI unit installation limitations.
With reference to FIG. 1, a power injector system 10 for injecting image-enhancing contrast media into a patient before or during an MRI scan is depicted as installed in an MRI suite 12. In particular, the power injector system 10 depicted is an OPTISTAR™ magnetic resonance (MR) digital injection system available from Mallinckrodt, Liebel-Flarsheim Business, Cincinnati, Ohio. The system 10 successfully operates within an MRI suite 12 by placement of components at varying distances from an MRI unit 14 or with varying degrees of shielding. In particular, a power head 16 contains ultrasonic motors. The ultrasonic motors operate syringes to dispense contrast media and saline solution into a patient as commanded and powered over a shielded power head cable 18 by a power control 20.
The power control 20 is also within a shielded magnet room 22 of the MRI suite 12 along with the power head 16 and the MRI unit 14, although generally spaced away from the MRI unit 14 to reduce the EMIC considerations. Since AC outlets are generally not available in the shielded magnet room 22, the power control 20 is battery powered. The power control 20 provides power to the power head 16 in response to data signals that are relayed from the power head 16 to the power control 20 and between the power control 20 and a touch-screen console 24 outside of the shielded magnet room 22. In particular, a shielded electrical cable 26 for transferring data signals couples the power control 20 to an opening, such as a free hanging D-shell connector 28, in a penetration panel 30. An electrical cable 32 outside of the shielded magnet room 22 is electrically coupled to the other electrical cable 26 inside the shielded magnet room 22 via a filter 34 connected to the penetration panel 30. The filter 34 reduces RF noise induced on the cables 26, 32. In the depicted MRI suite 12, the cable 32 passes from an equipment room 36 that is positioned adjacent to the penetration panel 30 to a control room 38 where the MRI unit controls (not shown) and the power injector touch-screen console 24 reside.
Since the power control 20, and thus the power head 16, are battery powered, a battery charger 40 is placed in the control room 38 for recharging a battery 42 for use in the power control 20. The battery charger 40 receives its power from an AC outlet 44. Thus, an inconvenient task is placed on operators of the MRI unit 14 and battery-powered injector system 10 to monitor the state of charge of batteries 42 and swap batteries between the battery charger 40 and the power control 20. If an undercharge of batteries 42 installed in the power control 20 is not detected in a timely fashion, the operation of the MRI unit 14 is delayed, reducing the number of patients that may be scanned. Such reduction in the number of patients increases medical costs and limits delivery of medical services.
In addition to clinical and staffing considerations, there is the increased inventory of batteries 42 necessary to have sufficient batteries for both use and simultaneous recharging. Furthermore, use of battery power places design constraints upon the battery-powered injector system 10, such as reducing functionality or increasing the size and cost of the batteries 42 to handle the power demand.
As an example of a design constraint, the power control 20 provides power for the electronic components and the ultrasonic motors of the power head 16 and the electronic components of the power control 20 itself. The power control 20 does not power components outside the magnet room 22. Consequently, several of the major components of the battery-powered injector system 10 each individually have internal power supplies that regulate and convert electrical power for use by that major component. For example, the console includes a power supply that also receives power from the AC outlet 44 and converts the AC electrical power to DC voltages useful for the electronics and display devices therein. Similarly, the battery charger 40 includes an internal power supply that regulates and converts AC power to voltages suitable for its electronics and for the battery 42 being recharged. Also, the power control 20 includes an internal power supply for regulating and converting the battery power from installed batteries 42 for the voltages required for its operation. Each internal power supply increases the cost, the size, and the cooling requirement of each major component.
Therefore, a significant need exists for an MR injector system with reduced cost that is simpler to operate than current battery-powered injector systems.